1. Field of the Invention
The present invention is micromechanical device on the order of 100 xcexcm to 10 mm for indicating whether a shock has occurred, particularly detecting the presence of a shock when mounted to a package or object. More particularly the present invention is a no-power shock sensor that can be queried to indicate if the package or object has been subjected to a shock above a predetermined threshold.
2. Description of the Related Art
Shock sensors are used in many applications to monitor or detect shock forces imparted to an object that is fragile, under investigation, or of great value. Prior art shock sensors are frequently accelerometers utilizing sensing materials placed on a thin diaphragm with a proof mass attached to the diaphragm. Some of these devices also utilize materials having a piezoelectric effect, wherein the proof mass is carefully balanced above and below the diaphragm to avoid cross-axes sensitivity. One frequent use of mechanical shock detection devices is in the field of indicator alarms. Such alarms include those for sensing movement, time, temperature and a number of other physical parameters. Examples of such alarms include U.S. Pat. No. 5,506,568, which discloses a sensor for security systems that can sense sonic shocks and distinguish between natural sounds and the sound of a break-in; and U.S. Pat. No. 5,585,566, which discloses a shock detector for measuring intermittent shock events to assist in position tracking. One specific use of a mechanical shock detection device is for shipping where the sensor, mounted upon a package, will provide an indication of possible damage which occurs during shipment as a result of rough handling. One example of such a sensor can be found in U.S. Pat. No. 6,104,307, which discloses a condition responsive alarm system having a mount with an adhesive on the rear face and including a power source secured to the mount. A second example of such a sensor may be found in U.S. Pat. No. 5,811,910 which uses the piezoelectric material discussed above in order to detect shock in any direction.
However, for certain types of packages, including the shipment of warheads and explosives, the above referenced shock detection devices do not meet necessary size requirements, i.e. they are too heavy, and they all require power sources, which could present safety hazards when placed near explosive materials as well as lifecycle and reliability problems. Therefore, a shock sensor is desired that can detect a wide range of mechanical shock, yet is light weight and requires no external power source to operate.
The invention consists of a micromechanical device for sensing shock applied to packages containing explosives, weapons, or warheads. It is of particular importance to have information regarding forces that have been applied to explosives, weapons, or warheads during their transport both for safety reasons and to ensure that the explosive, weapon, or warhead operates properly when deployed during a critical mission. Current sensors do not meet the specific requirements for such a mission due to their heavy weight and because current sensors require their own power supply in order to operate. This invention was developed to address the above referenced need.
Accordingly, it is the object of this invention to provide a micromechanical shock sensor that is light weight.
It is a further object of this invention to provide a micromechanical shock sensor that requires no external power source.
It is a still further object of this invention to provide a micromechanical shock sensor that operates over a wide range of forces and in multiple directions.
This invention accomplishes these objectives and other needs related to detecting shock by providing a micromechanical shock sensor that is formed on the surface of a micro-substrate. A moveable proof mass is formed on the surface with at least one spring connected to the proof mass and the surface. The spring allows the proof mass to move a predetermined distance with a specified amount of resistance. Latching means are formed on the surface the predetermined distance from the proof mass. When the sensor is subjected to a sufficient shock, the proof mass moves and contacts the latching means. An indicator means is provided to allow this contact to be readily known by the user.